Control for electric welding apparatus



. Feb. 25, 1941'.

C. H. MURRAY Er AL CONTROL FOR ELECTRIC WELDING APPARATUS Filed July 14,1938 2 Sheets-Sheet I 1727757222112- JZWaraffMrrq;

flrerz: H. Fram /7 Feb. 25, 1941. C MURRAY 2,233,177

CONTROL FOR ELECTRIC WELDING APPARATUS Filed July 14, 1938 2Sheets-Sheet 2 J izcvavzfonr kg ardmrray Patented Feb. 25, 1941 OFFICECONTROL FOR. ELECTRIC WELDING APPARATUS Clifford H. Murray and HerbertA. Trussell, Worcester, Mass.

Application July 14, 1938, Serial No. 219,250

3 Claims.

The present invention relates to electric welding apparatus, and has forits object to provide an improved arrangement for accurately controllingthe flow of current in electric welding operations, particularly spotwelding.

According to the present invention, there is provided an improvedcontrol arrangement, simple and efiective in operation, whereby theduration of the flow of alternating current to the welding electrodescan be regulated over a wide range, running from a portion of a cycle toany desired number of cycles of an alternating current wave. The controldevices employed for carrying out the invention are driven insynchronism with the frequency of the alternating current source whichsupplies the welding circuit, and the invention contemplates theprovision of suitable adjustments of the control apparatus which can bequickly and conveniently made, to obtain the desired welding effectswhen operating on work employing difierent metals of varyingthicknesses. The above and other advantageous features of the inventionwill'hereinafter more fully appear from the following descriptionconsidered in connection with the accompanying drawings, in which-- Fig.1 is a diagrammatic view, illustrating the control arrangement and thecircuit connections associated therewith.

Fig. 2 is a view in side elevation of the motordriven apparatusillustrated diagrammatically in Fig. 1.

Fig. 3 is a view in front elevation of the parts shown in Fig. 2.

Fig. 4 is a schematic diagram, illustrating adjustment of the weldingperiod.

Fig. 5 is a fragmentary sectional view along the line 5-5 of Fig. 3.

Referring to Fig. 1, a source I of alternating current is provided toenergize a welding circuit, comprising conductors 2 leading to theterminals of the primary winding 3 of a welding transformer T. Thetransformer T provides a secondary winding 4, the terminals of which areconnected to the welding electrodes 5, in the usual manner.

For the purpose of connecting the terminals of the primary winding 3 tothe power conductors 2, a pair of contactors 6 are provided that areidentical in construction, and in operation. Each contactor 6 providesan operating winding 1 and a bridging member 8 which, when the winding 1is energized, serves to close the gap between a pair of normally opencontacts 9. One contact 9 of each pair is connected to the terminal ofthe primary transformer winding 3, while the other contact 9 isconnected to the power conductors 2 through the normally closed contactsII) of contactors II.

The contactors II are for the purpose of disconnecting the transformerwinding 3 irom the power conductors 2, and are identical in construc-.tion and in operation. Each contactor II provides an operating windingI2 and a bridging member I 3, that normally extends across the gapbetween the contacts I0, when the winding I2 is deenergized. Therefore,with both pairs of contactors B and II deenergized, prior to a weldingoperation, there exist gaps in the circuit of the primary winding at theopen contacts 9, and separate means for creating additional gaps, atcontacts I0, in the circuit of the winding 3, when the contactors 6 areclosed.

One terminal of each of the several contactor windings I and I2 isconnected to a common conductor I4, that is adapted to be connected to asupply main I5, energizable from one side of a suitable direct currentsource I6. For the purpose of energizing the conductor I4, a rwntactorI! is provided, comprising a winding i8, and a bridging member I9normally out of engagement with spaced stationary contacts 20 when thewinding I8 is deenergized. One contact 20 is connected to the conductorI4 leading to the contactor windings I and I2, while the other contact20 is connected to the direct current supply main I5. The supply main I5is adapted to be connected to the direct current source I6 by a switch2|, shown as providing normally open spaced contacts 22, engageable by abridging member 23 only when the switch 2| is operated to bring about awelding operation, under the automatic control of apparatus which willnext be described.

One terminal of the winding I8 of contactor I1 is connected to thesupply main I5, while the other terminal thereof is connected to astationary contact 24, forming part of a make-andbreak device, generallydesignated by the reference character 25. The device 25 also comprisesan arm 26, pivoted on a shaft 21, with the arm 26 electrically connectedto a supply main 28, energized from the opposite side of the directcurrent source 16, from which the main I5 is adapted to be energized. Aspring 29 tends to turn the arm 26 in the direction of the stationarycontact 24, and the engagement or disengagement of the arm 26 withcontact 24, depends upon the cooperation between an extension 26a of thearm 26 and a control element 33, rotatably mounted on a shaft 3| Thecontrol element 33 is in the form of a disk, and when the end of the armextension 23a is riding on the circular portion of the element, theopposite end of arm 28 is maintained out of engagement with the contact24, against the pull of spring 23. However, when the arm extension 26abears on a fiat portion 300 of the control member 30, the spring 23engages the arm 26 with the contact 24, to connect one terminal of thecontactor winding |3 with the supply main 23. However, the engagement ofarm 23 with contact 24, will not energize the contactor l1, unless theswitch 2| has previously been closed for the performance of a weldingoperation, and the main l5 thereby energized.

As previously pointed out, one terminal of each of the windings 1 ofcontactors 3 is connected to the common conductor l4, and the otherterminals of these windings are connected to a common conductor 32leading to a stationary contact 33, forming part of a make-and-breakdevice 34, associated with the device 25. The device 34 provides an arm35, pivotally mounted on the same shaft 21 carrying the arm 26, and aspring 33 tends to move the end of arm 35 in the direction of contact33. A second control element 31, also mounted on the shaft 3|, is in theform of a disk cooperating with an extension 35a of arm 35, to maintainthe other end of the arm out of engagement with the contact 33. Thecontrol element 31 provides a flat portion 31a which, when engaged bythe arm extension 35a, permits the spring 33 to engage the arm 35 withstationary contact 33, to connect one terminal of each contactor winding1 with the continuously energized direct current supply main 23.However, engagement of the contact 33 by arm 35 will not energize thewindings 1, unless at that moment the conductor I4 is energized byclosure of contactor |1, under the control of element 30.

One terminal of each of the windings l2 of the contactors H is connectedby a conductor 33 to a stationary contact 33 forming part of amakeand-break device 43, cooperating with the previously describeddevices 25 and 34. This device 43 provides an arm 4|, also mounted onthe shaft 21 and connected to the supply main 23, with a spring 42'tending to turn the arm 4| toward the contact 33. An extension 41a ofthe arm 4| cooperates with a third control element 43, mounted on theshaft 3|, with the circular portion of the element 43 serving tomaintain the arm 4| out of engagement with stationary contact 33.However, when the extension 4|a engages a flat portion 430' on theelement 43, the spring 42 engages the opposite end of arm 4| with thecontact 33, to connect one terminal of each of the contactor windings l2with the direct current supply main 23. It is evident that suchengagement will not energize the contactors l I, unless at that momentthe contactor nu closed.

The shaft 3| carrying the three control, elements 33, 31 and 43,isdriven through suitable gearing d by a synchronous motor 44 connecteddirectly across the alternating current power conductors 2 by a switch45 and leads 46, sothat the motor 44 is continuously operating in exactsynchronism with the alternating current source As previously pointedout, successive operation of the make-and-break devices 25, 34 and 43 bythe control elements 33, 31 and 43, respectively, will not operate thecontactors ",3 and II, unless the switch 2| has previously been closed,to encrgize the main l5. While obviously the switch 2| can be closed atany time during the revolution of the motor shaft 3|, it will be assumedfor the purposes of the following description of the operation, that theswitch 2| has been moved to the dotted line position when the threecontrol elements mounted on the shaft 3| occupy the angular relationshown in Fig. 1, so as to bring about a sequence of operations effectiveto cause the flow of welding current between the electrodes 5, as willnext be described.

With the operators switch 2| closed, rotation of the control shaft 3| inthe direction of the arrow, to bring the parts into the position of Fig.1, causes the arm 26 to engage contact 24, as arm extension 260. bearson the flat portion 300. of the control element 33. When this occurs,the winding l3 of the contactor I1 is connected across the directcurrent supply mains l5 and 28, thereby causing the bridging member I!)to engage contacts 23. As the arm 26 passes ofi of the flat portion300., the circuit of the winding I3 is broken at the contact 24, but theprevious upward movement of the bridging member I3 has established aholding circuit for the winding |3. For this purpose, a switch arm 41,connected to the terminal of the winding l8 leading to the contact 24,is operable by the contactor plunger [3a, and normally, this arm 41 isout of engagement with a stationary contact 43 connected to the main 28.Therefore, when energization of the winding I8 by the control element 33causes the plunger 18a carrying the bridging member I3 to pull up to thedotted line position, the arm 41 engages contact 48, and establishes aholding circuit for the winding |8 that is maintained as long as theswitch 2| remains closed.

Continued rotation of the shaft 3| from the position of Fig. 1, causesthe arm 35 to engage the contact 33 as the arm extension 35a bears onthe flat portion 31a of the control element 31. When this occurs, acircuit is established from the main 23 through the conductor 32 to oneterminal of each of the contactor windings 1. Since the other terminalsof these windings are connected to the then energized conductor |4, bothcontactors 3 pull up, to cause their 'members 8 to bridge the respectivepairs of contacts 3, in circuit with the power conductors 2. Closure ofthe contacts 3 therefore energizes the primary winding 3 of thetransformer T, whereupon welding current flows between the electrodes 5,for a period determined by the angular relation between the control ele-1116:1128 31 and 43, as will be hereinafter pointed ou With the partsoccupying the position of Fig. 1, and with the shaft 3| rotating in thedirection of the arrow, it is evident that the control element 43 willcause the arm 4| to engage the contact 33 a predetermined time after thearm 35 engages the contact 33, to energize the contactors 3. When thecontact 33 is so connected to the main the resulting energization of thewindings |2 of both contactors causes the bridging members l3 to leavethe contacts l3, thereby breaking the circuit from the power conductors2, and interrupting the flow of welding current as the transformer T isdisconnected from the source In order to prevent the contactors 3 fromopening, as the arm extension 35a passes off the flat 31a, the plunger1a of each winding 1 operates a contact arm 43 that is connected to thesame terminal of the winding 1 that leads to the contact 33. Normally,this arm 43 is out of engagement with a stationary contact 50 connectedto the main 28, but upon pulling up of the bridging member 8 by plunger1a, a holding circuit forthewincling 1 is established, which ismaintained as long as the switch 2| and contactor |1 remain closedu Eachcontactor provides a similar interlock arm 5| connected to one terminalof the winding l2 leading to the contact 39, and normally maintained bythe plunger I2a. out of engagement with a stationary contact 52connected to the main 28. Therefore, engagement of the arm 5| with thecontact 52, upon pulling up of the bridging member l3, establishes aholding circuit for each winding l2, which is maintained as long as theswitch 2| and contactor |1 remain closed.

From the foregoing, it is apparent that following the closure of switch2|, the first complete revolution of the control shaft 3| will result insuccessive operation of the contactors l1, 6 and II in the order named,to bring about a flow of alternating current between the weldingelectrodes, for a period determined by the angular relation between thecontrol elements 31 and 43.

However, continued rotation of the shaft 3|, with the switch 2| stillclosed, will not result in any further flow of welding current due tothe flow of current through the contactor windings l2, by reason of theclosure of the interlock contacts 5| and 52, as pointed out above. Thatis to say, as long as the contactors remain energized to maintain themain line contacts ||l open, the welding cycle cannot be repeated, eventhough the switch 2| remains closed through several revolutions of thecontrol shaft 3|.

Therefore, in order to obtain a second sequence of operations by thecontactors l1, 5 and II and cause another weld, it is first necessary toopen the switch 2|, whereupon all the contactors become deenergizedthrough disconnection of the main |5 from the source IS. The controlsystem is thereby restored to its normal non-operating condition, inreadiness to perform another welding operation, upon reclosure of theswitch 2|, at the will of the operator.

As previously pointed out, the invention contemplates the provision ofsuitable adjustments of the control apparatus described above, wherebythe period of time during which welding current flows, may be accuratelyvaried over a wide range, and one way of obtaining such adjustments is'shown in Figs. 3 and 5. For this purpose, the shaft 3| leading from themotor-driven reduction gearing G, has the control elements 30 and 31adjustably mounted thereon with a fixed angular relation between them,so that the pilot contactor I1 is always closed an appreciable intervalin advance of energization of the circuit making contactors 6, to startthe welding current. But the third control element 43, which operatesthe circuit breaking contactors II to interrupt the welding current, isfixed on the shaft 3|. In order to regulate the duration of the flow ofwelding current, provision is made for varying the angular relationbetween elements 43 and 31, to which end a clamping ring 53 is mountedon the shaft 3|, and a nut 54 threaded onto the end of the shaft 3|,provides a shoulder 55 bearing on the ring 53, see Fig. 5. The nut 54provides an enlarged knurled portion 56, whereby it may be readilyturned by hand, to tighten the clamping ring 53 and hold the element 31in position after an adjustment has been made with respect to element43.

Provision is also made for the relative adjustment between themake-and-break device 40 and the control element 43, so as to insurethat the contactors II will operate to open the circuit of the primarytransformer winding 3 at substantially the zero point on the currentwave of a cycle of alternating current. the shaft .21 carrying theseveral arms of the make-and-break devices, is mounted on a disk 51,through which the shaft 3| freely passes. The several stationarycontacts 24, 33 and 39, are also supported on the disk 51 by means of abar 53, from which the several contacts are insulated. The disk 51 issupported so as to be 'angularly adjustable about the axis of the shaft3| by diametrically opposed bolts 59 extending through slots 60equidistant from the axis of the shaft 3|, and e'ach having a center ofcurvature at the axis. The bolts 59 are threaded into a stationarybracket 5|, so that the disk 51 carrying the make-and-break devices maybe angularly adiusted with respect to the shaft 3|, to closely determinethe instant at which the arm 4| engages the contact 33, to energize thecontactors H and interrupt the welding current.

As previously pointed out, reduction gearing G is interposed between themotor and the control shaft 3|, and the ratio of this gearing is 'chosenso that the length of each adjusting slot 50 substantially correspondsto the angle through which the shaft 3| is turned during a completealternating current cycle. For example, assuming that the alternatingcurrent source is operating at 60 cycles, so that the synchronous motoris running at 3600 R. P. M., a reduction through the gearing G of 15 to1, will drive the shaft 3| at 240 R. P. M., or 4 revolutions per second-Therefore, the shaft 3| will be turned through 1440 angular degreespersecond, or at the rate of 24 for each cycle of alternating current.Using the above figures for purposes of illustration, it is evident thenthat with each slot 60 laid out to subtend an angle of approximately 24,it will be possible to find and maintain an angular position of the disk51, at which the arm 4| will engage the contact 39 so as to open thewelding circuit substantially at the zero point of an alternatingcurrent wave, with a consequent reduction of arcing at the contacts Into a minimum.

Assuming that the disk 51 has been set and clamped by means of the bolts59, so as to assure opening of the welding circuit at the zero point ofthe current wave, it is then an easy matter to adjust the element 31with respect to the element 43, to obtain the desired duration of theflow of welding current. As previously pointed out, each 24 of controlshaft displacement corresponds to the duration of one cycle of current,assuming a gear reduction of 15 to 1, and a 60 cycle source. Therefore,.by varying the angular position of control element 31 with respect tothe element 43, which is fixed on the shaft 3|, the duration of the flowof welding current can be varied from a portion of an alternatingcurrent cycle to several cycles. With an angular displacement betweenthe flat portions 31a and 43a of approximately 48, as shown in Fig. 1,it is evident that the welding current'will flow through the duration ofapproximately two alternating current cycles. Obviously, this durationof welding current can be diminished to a fraction or a cycle, by tumingthe element 31 against the direction of rotation of the shaft 3|, or theduration of welding To this end,

current flow can be carried through several cycles, by turning theelement 31 in the direction of control shaft rotation. If desired, theperipheral edge of the fixed element 43 may be calibrated in terms ofthe number of cycles of current flow, with reference to a zero markpassing through the middle of the fiat portion 43a, so that a pointer atthe middle of the flat portion 31a on element 31 will show theadjustment. It is to be noted that the figures given above are purelyarbitrary, being based on the assumption of a given gear reductionbetween the shaft of motor 44 and the control shaft 3|, and obviously,the particular angular displacement of the control shaft 3|,corresponding'to the duration of an alternating current cycle, can beincreased or decreased as desired, by varying the gear ratio.

With the duration of welding current flow closely adjustable over a widerange, as described above, it is evident that the apparatus of thepresent invention is adapted to control the electric welding ofdifferent kinds of material of varying thicknesses. That is to say, thewelding period can be cut down to a small fraction of a cycle, such as 5or of a second, as when welding very thin sheets of stainless steel,where the welding heat must be reduced to'avoid deterioration of themetal. 0n the other hand, the Welding period can be increased to extendthrough as many as fourteen cycles, with the figures given, so as togive a current flow of approximately of a second, as when welding sheetsof thick metal, such as boiler plate.

In order to obtain very close adjustment of the several make-and-breakdevices 25, 34 and 40, each of the stationary contacts 24, 33 and 39 ismicrometrically adjustable within the bar 53, as shown in Fig. 3,thereby making it possible to accurately time engagement ordisengagement of the arms 26, 35 and 4l, with the contacts 24, 33 and 33under the control of elements 30, 31 and 43, respectively. I

From the foregoing, it is apparent that by the present invention thereis provided an improved control arrangement, whereby the duration of theflow of alternating current to welding electrodes can be quickly andconveniently varied over a wide range, running from a portion of analternating current cycle to any desired number of cycles, to suit thecharacter of the metal work being welded. While in the drawings only oneset of electrodes is shown under the control of a set of timing elementsand contactors, obviously, the control shaft 31 can be extended to carryadditional sets of control elements, each adapted to regulate the flowof current through separate welding electrodes, independently of eachother. By the employment of separate contactors to make and break thecircuit of the welding transformer, extremely positive control of theflow of welding current is obtained, while the automatic functioning ofthe interlocking contactor circuits makes it impossible for the weldingcycle to be repeated, except by opening and reclosing the operatorsswitch 2|. If desired, the switch 2| could be automatically closed andopened at fixed intervals to give regular spacing of welds, as iscustomary in seam welding.

We claim,

1. In combination, a circuit to be controlled, a source of alternatingcurrent, a synchronous motor continuously energized from said source, a

control device rotatively driven by said motor comprising pairs ofrelatively movable contacts adapted to be successively closed andquickly opened once during each complete revolution of said controldevice, a relay providing normally open contacts in said circuit, asecond relay providing normally closed contacts in said circuit,connections between the control contacts and relays for successivelyenergizing said relays to close the contacts of the first relay and toopen the contacts of the second relay, after a predetermined period ofcurrent flow from the source measured in terms of alternating currentcycles. and additional connections for maintaining said relays in anenergized condition, independently of said control contacts, to limitthe flow of current in said circuit to a single period, irrespective ofthe continued rotation of said control device by said motor.

2. In combination, a circuit to be controlled, a source of alternatingcurrent, a synchronous motor continuously energized 'irom said source, acontrol device rotatively driven by said motor comprising pairs ofnormally open contacts adapted to be momentarily closed in successionduring each complete revolution of said control device, a relayproviding normally open con tacts in said circuit, a second relayproviding normally closed contacts in said circuit, connections betweenthe control contacts and relays for successively energizing said relaysto close the contacts of the first relay and to open the contacts of thesecond relay, after a period of current flow from the source measured interms of a1ternating current cycles,means for adjusting said controldevice to vary the interval between the closing and opening of the relaycontacts over a predetermined number of alternating current cycles, orportions of cycles, and additional con nections for maintaining saidrelays in an energized condition independently of said control contactsto limit the flow of current in said circuit to a single period, inaccordance with the adjustment of said control device and irrespectiveof the continued rotation thereof by said motor.

3. In combination, a circuit to be controlled, a source of alternatingcurrent, a synchronous motor continuously energized from said source, acontrol device rotatively driven by said motor comprising pairs ofnormally open contacts adapted to be momentarily closed in successionduring each complete revolution of said control device, a relayproviding normally open contacts in said circuit, a second relayproviding normally closed contacts in said circuit, connections betweenthe control contacts and relays for successively energizing said relaysto close the contacts of the first relay and to open the contacts of thesecond relay, after a period measured in terms of alternating currentcycles, a third relay providing normally open contacts in the energizingcircuits of the first and second relays, connections between the controlcontacts and said third relay for closing its contacts in advance ofoperation of the other relays, and additional connections formaintaining all of said relays in an energized condition independentlyof said control contacts, to limit the flow of current in said circultto a single period, irrespective of the continued rotation of saidcontrol device by said motor.

CLIFFORD H, MURRAY. HERBERT A. TRUSSELL.

